Auditory brainstem response (ABR) latency shifts in animal models of various types of conductive and sensori-neural hearing losses.

Clinical ABR studies in patients with peripheral hearing loss have led to conflicting results, some reporting increases in brainstem transmission time (BTT), some decreases, and others no change. In order to study this in a carefully controlled fashion, various types of peripheral hearing losses were induced in experimental animals: conductive hearing loss by occluding auditory meatus (rats) (CHL), noise induced temporary sensori-neural hearing loss (rats) (NI-SNHL), stimulus intensity attenuation (rats), (Atten.), and controlled hypoxemia induced temporary sensori-neural hearing loss (cats) (HI-SNHL). ABR latencies and thresholds were determined in each animal before (control) and during the induced hearing loss (experimental) states. The data in each group in each state were analyzed by calculating group average values for latency of waves 1 and 4, their interpeak latency (BTT), paired t-tests for changes between the control and experimental states and linear regression analysis of latency changes on threshold shift. In each group, there were small decreases in BTT in the experimental state (not significant in the CHL group only). This was caused by the prolongation of latency of wave 1 to a greater extent than that of wave 4. These changes were smaller than the standard deviation of the BTT in the control state. Therefore, in attempting to apply these results to the human clinical situation, these small decreases in BTT would not be considered abnormal. Possible mechanisms of these BTT changes are considered.